[PATCH 3/7] xfs: fix a bug in the online fsck directory leaf1 bestcount check

Darrick J. Wong
2021-12-16T01:09:35Z

From: Darrick J. Wong <djwong@kernel.org>

When xfs_scrub encounters a directory with a leaf1 block, it tries to
validate that the leaf1 block's bestcount (aka the best free count of
each directory data block) is the correct size. Previously, this author
believed that comparing bestcount to the directory isize (since
directory data blocks are under isize, and leaf/bestfree blocks are
above it) was sufficient.

Unfortunately during testing of online repair, it was discovered that it
is possible to create a directory with a hole between the last directory
block and isize. The directory code seems to handle this situation just
fine and xfs_repair doesn't complain, which effectively makes this quirk
part of the disk format.

Fix the check to work properly.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/scrub/dir.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/scrub/dir.c b/fs/xfs/scrub/dir.c
index 200a63f58fe7..9a16932d77ce 100644
--- a/fs/xfs/scrub/dir.c
+++ b/fs/xfs/scrub/dir.c
@@ -497,6 +497,7 @@ STATIC int
xchk_directory_leaf1_bestfree(
struct xfs_scrub *sc,
struct xfs_da_args *args,
+ xfs_dir2_db_t last_data_db,
xfs_dablk_t lblk)
{
struct xfs_dir3_icleaf_hdr leafhdr;
@@ -534,10 +535,14 @@ xchk_directory_leaf1_bestfree(
}

/*
- * There should be as many bestfree slots as there are dir data
- * blocks that can fit under i_size.
+ * There must be enough bestfree slots to cover all the directory data
+ * blocks that we scanned. It is possible for there to be a hole
+ * between the last data block and i_disk_size. This seems like an
+ * oversight to the scrub author, but as we have been writing out
+ * directories like this (and xfs_repair doesn't mind them) for years,
+ * that's what we have to check.
*/
- if (bestcount != xfs_dir2_byte_to_db(geo, sc->ip->i_disk_size)) {
+ if (bestcount != last_data_db + 1) {
xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, lblk);
goto out;
}
@@ -669,6 +674,7 @@ xchk_directory_blocks(
xfs_fileoff_t lblk;
struct xfs_iext_cursor icur;
xfs_dablk_t dabno;
+ xfs_dir2_db_t last_data_db = 0;
bool found;
int is_block = 0;
int error;
@@ -712,6 +718,7 @@ xchk_directory_blocks(
args.geo->fsbcount);
lblk < got.br_startoff + got.br_blockcount;
lblk += args.geo->fsbcount) {
+ last_data_db = xfs_dir2_da_to_db(mp->m_dir_geo, lblk);
error = xchk_directory_data_bestfree(sc, lblk,
is_block);
if (error)
@@ -734,7 +741,7 @@ xchk_directory_blocks(
xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, lblk);
goto out;
}
- error = xchk_directory_leaf1_bestfree(sc, &args,
+ error = xchk_directory_leaf1_bestfree(sc, &args, last_data_db,
leaf_lblk);
if (error)
goto out;